Drosophila melanogaster populations from North Carolina and Great Britain were sampled to determine the frequency of null alleles at 25 allozyme loci. Nulls were found at 14 of 20 autosomal loci with a weighted mean frequency of 0.0024, with a range from 0.00 to 0.01. No nulls were found at five X-chromosome loci. The frequencies and between locus comparisons suggest that null alleles are maintained in mutation selection balance. The data also indicate that allozyme loci are not characteristic of the whole genome.